On 01/22/2016 10:59 AM, Michael Ellerman wrote:

On Thu, 2016-01-21 at 21:45 +0530, Vasant Hegde wrote:

quoted

With commit 90a545e9 (restrict /dev/mem to idle io memory ranges) mapping
rtas_rmo_buf from user space is failing. Hence we are not able to make
RTAS syscall.

This patch calls page_is_rtas_user_buf before calling iomem_is_exclusive
in  devmem_is_allowed(). This will allow user space to map rtas_rmo_buf
and we are able to make RTAS syscall.

Michael,

Thanks for the patch.

I'll put it in my fixes branch for next week.

Thanks!

Having said that, why the <expletive deleted> is librtas mapping /dev/mem in
the first place? Unless there is a very good reason, and probably even if there
is, we should fix that to use a sane API.

We use rtas system call. We use /dev/mem interface to map the RTAS memory region
(allocated by kernel and information is passed to user space via procfs) so that
we can read/write to RTAS memory.

I do not have historical information. May be Nathan has more information on this.

-Vasant